The present invention relates generally to a paper skew removal apparatus for use in a paper feeder, and, in particular, to a paper skew removal apparatus for use in a printer that will reduce the printer size and speed up print time, and a technique for removing the skew of paper in a paper feeder.
Generally, various types of paper skew removal apparatuses have been proposed. FIGS. 20(a)-20(c) illustrate a paper skew removal apparatus described in Unexamined Japanese Patent Application No. Hei. 1-141070. The paper skew removal apparatus includes a platen 2 positioned orthogonal to an advancing direction A of a paper P fed by paired paper feed rollers 1, 1. The axis of platen 2 is parallel to the axis of each of the paired paper feed rollers 1, 1. When leading edge Pa of paper P advances and contacts platen 2, a slack loop Pb forms in paper P as shown in FIG. 20(b). The slack loop Pb absorbs a skew of the paper. Thereafter, platen 2 rotates in a clockwise direction so as to feed paper P as shown in FIG. 20(c). With platen 2 rotating in the clockwise direction, and paper P moving in the direction as indicated by arrow A, paired paper feed rollers 1, 1 rotate in the clockwise direction and a slackened part Pb', having absorbed the skew, gradually disappears.
Another paper skew removal apparatus, shown in FIGS. 21(a)-21(c), is described in Unexamined Japanese Patent Publication No. Hei. 2-62348. FIG. 21(a) shows a single long paper feed roller 3 and a discharge film 4 which interact with each other to feed paper P while pressing the paper over its full width. A pair of rollers 5, 6, positioned downstream of the combination of paper feed roller 3 and discharge film 4, are arrayed orthogonal to the advancing direction A of paper P. A leading edge Pa of paper P moves in the direction as indicated by arrow A and contacts a nip T between stationary paired rollers 5, 6. Then, as shown in FIG. 21(b), paper P is turned in the direction of an arrow B. As a result, the paper skew is removed and the paper is orientated as shown in FIG. 21(c).
The conventional paper skew removal apparatuses employing the structures described above have the following problems.
In the paper skew removal apparatus of FIG. 20, a slack loop Pb of paper P must be formed between paired paper feed roller 1, 1 and platen 2. Accordingly, a large space must be provided between paired paper feed roller 1, 1 and platen 2, and there is a long delay before paper P reaches platen 2. Formation of slack loop Pb after the paper reaches platen 2 also delays printing.
Thus, the paper skew removal apparatus of FIG. 20 has too long a paper feed time. Further, the size of the paper skew removal apparatus is large since paired paper feed roller 1, 1 and platen 2 must be positioned sufficiently away from each other in order to form the slack loop.
Furthermore, the paper skew removal apparatus described in FIG. 21 is constructed and arranged so that discharge film 4 cooperates with single long paper feed roller 3 to press the paper over its full width. Therefore, the paper skew removal apparatus has difficulty rotating paper P to remove the skew because of the pressure upon paper P over its full width.
Accordingly, it is desired to provide an improved paper skew removal apparatus which has a reduced paper feed time, a reduced size, and is capable of reliably removing a skew from the skewed paper.